Gaseous discharge lamp



D. MCF. MOORE GAsEoUs DISCHARGE LAMP Aug. 28, 1934.

Filed Deo. 31. 1950 Inventor:

Daniel MoFarlan Moore,

um His Attorney.

Patented Aug. 28,l 1934 PATENT OFI-'ICE 1,971,916 GAsEoUs DISCHARGELA'MP Daniel McFarlan Moore, East Orange, N. J., assignor to GeneralElectric Company, a corporation of New York Application December 31,1930, Serial No. 505,847

4 Claims.

The present invention relates to gaseous electric discharge devices ofthe positive column type, such for example, as lamps in which a luminousdischarge is produced in a column of attenuated gas.

When an electric discharge is produced in a gas at low pressure underconditions producing lumi-- nosity in a column of gas between theelectrodes of the discharge the fall of potential at the cathode dependslargely on the production of electrons at the cathode. If electrons areonly produced by the discharge between the main electrodes, a relahtively high fall of potential occurs at the cathode. In luminousdischarge lamps, such as used. commonly for display lighting, providedwith nonthermionic cathodes, the fall of potential at the cathode is ofthe order of several hundred volts. Such a high fall of potential iswasteful'of energy and renders such lamps unsuitable for operation atcommercial lighting voltages.

As a consequence of my present invention I have provided gaseousdischarge devices in which an abundant supply of electrons for apositive column gas discharge is generated by an auxiliary discharge,rendering such lamps operable with a cathode fall of potential of about90 volts. Positive column lamps embodying my invention are operable atcommercial distribution voltages without the starting devices heretoforerequired.

The novel features of my invention will be described in greater detailin connection with the accompanying drawing in which Fig. 1 is alongitudinal section of an alternating current lamp embodying myinvention; Fig. 2 is an end view of the electrode structure for oneterminal of the lamp shown in Fig. 1; Fig. 3 is a similar View of adirect current lamp; Fig. 4 is a side view partly in section of amodification; Fig. 4A is an end view of the electrodes of Fig. 4; andFig. 5 is a longitudinal section of a modified water-cooled cathodestructure.

The lamp shown in Fig. 1 comprises an elongated envelope 1 consisting ofglass, or like material.l It has been shown as broken, as ordinarily itis of greater length than can be illustrated on the scale of drawingwhich has been adopted. It should be understood, however, that thebenefits of my invention are obtainable also in lamps having a shortpositive column.

The envelope contains a suitable filling of gas or a gaseous mixture inwhich a desired luminous discharge may be produced. For example, the gascharge may consist of neon, preferably admixed with about 3/8% argon,and the gas preferably should be at a pressure within the range of about10 to 20 millimeters of mercury. In the preparation of the lamp theenvelope and-electrodes should be freed from deleterious gases inaccordance with the known technique. In general, the preparation andnature of the gaseous filling should follow the practice now wellunderstood in the art.

The electrode structure shown at opposite ends of the lamp is asubstantial duplicate, hence the structure for but one end will bedescribed, the same reference numerals primed being applied to thestructure at the opposite end. The electrode structure at opposite endscomprises an electrode 2 consisting of tungsten, iron, aluminum, copper,magnesium or other suitable metal and encloses an electrode 3 ofsomewhat greater length, which can also be made of aluminum or copper ortungsten or magnesium or other suitable metal. The two electrodes areseparated by a layer 4 of electrical insulation, which may consist offired magnesium silicate, mica, alumina, or the like. The exposed endsof the electrodes 2, 3 are flush with one another. The inwardlyprojecting flange 5 of the electrode 2 is separated by a narrow gap ormoat from the electrode 3 which preferably is so narrow that no visibledischarge occurs in it. Preferably the width of this gap is within thedimensions of the Crookes dark space. Both electrodes are provided withfunnel-shaped craters whereby the emission of electrons is facilitated.Only two craters are shown in the sectional view, Fig, 1, in electrode2, but usually there are eight such craters in a circle as shown in Fig.2, or four such craters in each electrode, as shown in Fig. 4A, at 6,6b, 6c, and so on. The craters may be formed either in the body of theelectrode, or in an insert consisting of material of higher electronemissivity than the main portion of the electrode. For example, tofacilitate low break down voltage and copious electron emission suchinsert may consist of, or the walls of the crater may be coated with, analkaline earth metal, such as magnesium, or barium, or barium azide, orcaesium, or a rare earth metal, such as thorium, or cerium, or an alloysuch as ferrocerium, or Mischmetal. However when both electrodes 2 and 3are completely made of such specially selected metal, there is gainedthe additional advantage that material of the opposing walls of the moator electron gap assist in current flow at minimum potentials. Thecraters for most purposes may have a muzzle diameter of about 4/ 100 to6/ 100 of an inch and a depth of about lg inch.

The electrodes 2 and 2 at opposite ends of the tubular envelope 1 areconnected by the conductors 9, to a suitable source of alternatingcurrent, through a suitable series resistance 11, and

g a switch 12 is shown in the circuit. The electrodes 3, 3 are connectedto one another by a conductor 13 containing a resistor 14, or othersuitable impedance device, and a switch 15.- 'Ihe two gaps between theelectrodes 2, 3 and 2', 3' respectively are connected through thecircuit 13 in series across the line when the switch 15 is closed,causing a current of low value to ilow over the two electron gaps inseries with each other.

The lamps illustrated in the drawing have been shown merely asillustrative of my invention but my invention is broader than the lampsillustrated in the drawing. In general, it may be said that the luminousefficiency of such lamps depends largely on the ratio of the length tothe diameter of the positive column formed in the discharge tubeconnecting to'two electrode en' velopes. The light production andeiiciency in general varies directly with this ratio. For example, withan impressed voltage of 220 volts the maximum efficiency is obtained byusing a discharge tube that is as long as practicable and of as small adiameter as practicable for starting and operation at this voltage.'I'he following is one example of such a lamp operable at 220 voltsembodying my invention, although a great many modications may beemployed. Such a lamp for alternating current use may be constructed asshown in Fig. 1 the distance between the opposite sets of electrodesbeing about 121/2 inches and the glass discharge tube between them'beinginch in diameter. The diameter of the duplex electrode in the electrodeenvelope at each end of the lamp is about 1&2 inches, the diameter ofthe inner'electrode being about 1A, inch.

No current will flow through the lamp of Fig. 1 when switch 12 is closeduntil switch 15 in the auxiliary circuit 13 is also closed. The currentthen owing across the gaps between the paired electrodes at oppositeends of the lamp produce an emission of electrons sufficient to startand carry the main discharge in the 5/8" glass discharge tube, althoughthe current through this auxiliary circuit 13 is only about .013 ampere,the resistance 14 being relatively high, for example, about 1000 ohms.Assuming the series line resistance l1 to be about 45 ohms, currentthrough the positive column will be about 0.8 ampere. With a gas fillingconsisting mainly of neon the resulting positive column discharge givesa brilliant light.

The number of amperes owing through this positive column of given lengthand diameter can be regulated by varying either the amount of the seriesresistance 11 in circuit with the main electrodes or the amount of theresistance 14 in series with the electron-emission gaps at theelectrodes. If no resistance is provided in this auxiliary circuit 13and if the areas of the electrodes exposed in the gaps are too large,ythen too much current will flow across the gaps, thus dellecting undueamounts of energy from the positive column. In general, it may be saidthat the current in the auxiliary circuit, the size and shape of theelectrodes, and the number of craters in the cathodes should be sochosen that the main current through the positive column is properlymaintained.

'I'he direct current lamp illustrated by Fig. 3

other `means for independently emitting electrons. 'Ihe main electrode18, 2 of this lamp are connected to a direct current source respectivelyby the conductor 17, and the conductor 18. In the circuit 13 connectingthe electrodes 16 and 3 is a resistor 14.

In the alternating current lamp illustrated in Fig. 4 the discharge tubein which the positive column discharge is produced is bent into the formof a U and is mounted within an outer envelope 20. The craters in theelectrodes are shown above the main figure. Four craters are indicatedat 21 in the outer electrode 2 but a different number may be employedaccording to circumstances. The inter-electrode auxiliary circuit 13 andits resistor 14 are embodied Within the lamp structure. If the gapsbetween the two sets of electrodes are suitably proportioned to the restof the lamp the resistor 14 may be made small and even may be omittedentirely. The electrodes 3, 3 of Fig. 4 may be connected to a suitablealternating supply circuit by the conductors 9, 10'which are shownconnected to a conventional lamp base.

Fig. 5 illustrates an electrode structure `oi a lamp oi highercurrent-carrying capacity which is provided with means for artificiallycooling the crater electrodes. The discharge tube has been shown brokenaway.

The structural features of the cathode shown in Fig. 5 in many respectsare similar to the structural features already described in connection'with the other iigures. It will be noted, however, that the lower endof the cathode 22 terminates in a sharpened rim or edge which is sealeddirectly to the tubular glass envelope 23. Surrounding the electrodechamber is an outer jacket 24 through which the cooling fluid such aswater is circulated through inlettube 26 and outlet tube 25. Anelectrical connection to the cathode 22 is made through conductor 26which terminates in compressible spring 27, the outer end of which makeselectrical contact with the electrode 22. Contact to the anode 28 ismade through a side arm 29 by anode conductor 30. The glass electrodechamber or envelope 23 is jointed at its right hand end to a tube whichis shown broken away and through which the brilliant positive columndischarge occurs. A similar structure may be employed at opposite endsof the positive column when alternating current operation is desired andthe electrical connections will correspond to those of Fig. 1. Otherwisean ordinary anode, such as shown at 16, Fig. 3, is employed inconnection with such a water-cooled cathode on a direct current 'circuitand the electrical connections will correspond with Fig. 3.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:-

1. An electric lampA comprising anenvelope, a luminosity-producing gastherein, a main anode, a main anode provided with one or more cratersand a cooperating auxiliarycathode located closely adjacent said cratercathode, said auxiliary anode also being provided with one or morecraters.

2. An electric lamp .comprising an elongated envelope, adischarge-conducting gas therein. cooperating main electrodes atopposite ends of said envelope for supporting a discharge through saidgas, one of said electrodes being provided with a crater and anauxiliary electrode also provided with a. crater spaced closely adjacentsaid main crater electrode and electrical connections for saidrespective crater electrodes whereby independently of said maindischarge an auxiliary discharge may be produced which lls said craterwith luminosity.

3. A gas conduction device comprising a closed envelope containing anattenuated gas of good conductivity, a main anode, a main cathode spacedapart a suicient distance to produce a long positive column dischargetherebetween, said main cathode having one or more funnel-shapedindentations in the surface thereof, a third electrode spaced from saidmain cathode a distance substantially equal to the Crookes dark spaceand a. circuit connected electrically in parallel to the gas spacebetween said electrodes for producing a luminous discharge between saidmain cathode and said third electrode emanating from one or more of saidcraters.

4. The combination in an electrical discharge device of a unitarystructure comprising an elongated envelope, a plurality o! electrodes atone end of said envelope, each having a funnel-shaped crater Yformedtherein. material of high electron emissivity lining the walls of saidcrater, means for electrically insulating said electrodes from oneanother, separate leading-in conductors for said electrodes, and anotherelectrode at the opposite end of said envelope.

DANIEL McFARLAN MOORE.

